function addRollover(img, rolloverURL) {
  if (typeof img == "string") {
    var id = img;
    img = null;
    
    if (document.getElementById) img = document.getElementById(id);
    else if (document.all) img = document.all[id];
    
    if (!img) img = document.images[id];
    
    if (!img) return;
  }
  
  if (img.tagName.toLowerCase() != "img") return;
  
  var baseURL = img.src;
  (new Image()).src = rolloverURL;
  
  img.onmouseover = function() { img.src = rolloverURL; }
  img.onmouseout = function() {img.src = baseURL; };
}

function initRollovers() {
  var images = document.getElementsByTagName("img");
  for (var i=0; i<images.length; i++) {
    var image = images[i];
    var rolloverURL = image.getAttribute("rollover");
    if (rolloverURL) addRollover(image, rolloverURL);
  }
}